U.S. Pat. No. 3,730,727 (developing solutions comprising a combination of ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (use of hydrazine as a auxiliary developing agent for providing a direct positive color image), U.S. Pat. No. 3,386,831 (use of .beta.-monophenylhydrazide of aliphatic carboxylic acid as a stabilizer for silver halide light sensitive materials), U.S. Pat. No.2,419,975, and Mees, The Theory of Photographic Process, 3rd ed., 1966, page 281, disclose the use of hydrazine compounds in a silver halide photographic emulsions or developing solutions.
In particular, it is disclosed in U.S. Pat. No. 2,419,975 that a high contrast negative image can be obtained by the incorporation of a hydrazine compound.
The patent discloses that when a light-sensitive material comprising a silver bromochloride emulsion containing a hydrazine compound incorporated therein is developed with a developing solution having a high pH value such as 12.8, an extremely high contrast having a gamma value of more than 10 can be provided. However, strongly alkaline developing solutions having pH values of near 13 are susceptible to air oxidation and are unstable, they are therefore, unsuitable for prolonged use or storage.
An ultra-high contrast wherein a gamma value is more than 10 is extremely useful for the photographic reproduction of continuous tone images or the reproduction of line images by dot image processing which is useful for photo-engraving making regardless of whether negative images or positive images are formed. For this purpose, a light-sensitive material comprising a silver chloride content of 50 mol % or more and preferably 75 mol % or more, has been developed with a hydroquinone developing solution having an extremely low effective concentration of sulfinic ion (normally 0.1 mol/l or less). However, because of its low sulfinic ion concentration, such a developing solution is extremely unstable and defies prolonged storage (e.g., more than 3 days).
Furthermore, these methods require the use of a silver bromochloride emulsion having a rather high silver chloride content and thus cannot provide high sensitivity. It has, therefore, been desired to obtain ultra-high contrast useful for reproduction of dot images or line images using a high sensitivity emulsion and a stable developing solution.
The Inventors have disclosed a silver halide photographic emulsion which is developed with a stable developing solution to provide an extremely high contrast (see U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614 and 4,323,643). However, it has been found that the acyl hydrazine compounds used in these emulsions have some disadvantages.
For example, the hydrazines have been known to produce nitrogen gas during development. The nitrogen gas forms bubbles in the film which damage photographic images. Furthermore, the nitrogen gas flows into the developing solution, adversely effecting other photographic light-sensitive materials.
Furthermore, these hydrazines are disadvantageous in that they need to be used in large amounts to provide sensitization and higher contrast. These hydrazines are also disadvantageous in that when they are used in combination with other sensitizing technics (e.g., to increase chemical sensitization, increase grain size, sensitization accelerating compounds as described in U.S. Pat. No. 4,272,606, and 4,241,164 may be added) to render the light-sensitive material more sensitive, sensitization and/or fogging may occur during the storage of the light-sensitive material.
Therefore, it would be beneficial to provide a compound which can reduce bubble production and the flow of bubbles into the developing solution, which causes no stability problems with time, and can be used in extremely small amounts to provide high contrast.
U.S. Pat. Nos. 4,385,108, 4,269,929 and 4,243,739 indicate that hydrazines containing substituents which are easily adsorbed by silver halide grains can be used to obtain extremely high contrast negative gradation. Among hydrazine compounds containing such adsorption groups, the specific examples described above are disadvantageous in that they are subject to desensitization with time upon storage.
On the other hand, there are various direct positive photographic processes. Among these processes, the most useful are processes in which silver halide grains are exposed to light in the presence of a desensitizer, and then developed, and processes in which silver halide emulsions containing light-sensitive nuclei primarily within the silver halide grains are exposed to light, and then developed in the presence of a nucleating agent. The present invention relates to the latter type of process. A silver halide emulsion containing light-sensitive nuclei primarily within the silver halide grains which forms latent images therein is commonly referred to as an internal latent image type silver halide emulsion. This type of emulsion is distinguished from silver halide emulsions which form latent images primarily on the surface of silver halide grains.
There are known processes in which internal latent image-type silver halide photographic emulsions are surface-developed in the presence of a nucleating agent to provide direct positive images, as well as photographic emulsions or light-sensitive materials for use in such processes.
In the above described processes for the formation of direct positive images, nucleating agents have been incorporated in the developing solution. Also nucleating agents have been incorporated in the photographic emulsion layer or other proper layers in light-sensitive materials so that when it is absorbed by the surface of silver halide grains, better reversal properties can be obtained.
Examples of such nucleating agents include hydrazines such as those described in U.S. Pat. Nos. 2,563,785 and 2,588,982, hydrazide and hydrazine compounds such as those described in U.S. Pat. No. 3,227,552, heterocyclic quaternary salt compounds such as those described in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 4,094,683 and 4,115,122, British Pat. Nos. 1,283,835, and JP-A-Nos. 52-3,426, and 52-69,613 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), thiourea-bound acylphenylhydrazine compounds such as those described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511 and 4,276,364 and British Pat. No. 2,012,443, compounds containing as adsorption groups heterocyclic thioamide such as those described in U.S. Pat. No. 4,080,207, phenylacylhydrazine compounds containing heterocyclic groups comprising mercapto groups as adsorption groups such as those described in British Pat. No. 2,011,397B, sensitizing dyes containing in the molecular structure thereof substituents having a nucleating effect such as those described in U.S. Pat. No. 3,718,470 and hydrazine compounds such as those described in JP-A Nos. 59-200,230, 59-212,828 and 59-212,829 and Research Disclosure No. 23,510 (Jan. 1953).
However, these compounds for obtaining a negative image and positive image having high contrast have been found disadvantageous in that they provide insufficient activity as nucleating agents. Even when they provide sufficient activity, their preservability has been found to be insufficient. Their activity may be deteriorated by the time when it is coated on a support in the form of an emulsion. If they are used in large amounts, they deteriorate the properties of the prepared film.
For the purpose of solving these problems, there have been proposed nucleating agents disclosed in JP-A-No. 60-179734, JP-A-No. 61-170733, JP-A-No. 61-270744, JP-A-No. 62-65034, JP A-No. 62-948, JP A-No. 63-223744, JP-A-No. 63-234244, JP-A-No. 63-234245, JP-A-No. 63-234246, Japanese Pat. application Nos. 62-166117 and 62-143469. However, it is desired to provide agents having more higher nucleating activity, which meet requirements of lowering the pH of processing solution to enhance the stability of the developing solution (namely, to prevent developing agents from being deteriorated), shortening processing time in development or reducing change of compositions in the developing solutions (e.g., pH, sodium sulfite, etc.).